Up-Front Versus Delayed Thermal Ablation for Colorectal Liver Oligometastases: A Multicenter Retrospective Study Using Propensity Score Matching

BACKGROUND. Thermal ablation combined with systemic therapy is an accepted treatment of colorectal liver oligometastases (CLOM). Consensus is lacking regarding the optimal timing of thermal ablation relative to systemic therapy. OBJECTIVE. The purpose of our study was to compare delayed and up-front thermal ablation in terms of efficacy and safety in the treatment of patients with CLOM. METHODS. This retrospective multicenter study included 440 patients (316 men, 124 women; mean age, 57.1 +/- 11.1 [SD] years) with CLOM from nine hospitals between October 2009 and December 2020. Patients underwent delayed (n = 322) or up-front (n = 118) thermal ablation in combination with systemic therapy. Analyses included all patients using crude data, all patients using inverse probability treatment weighting (IPTW), and a subset of patients using propensity score matching (PSM) at a 1:1 ratio to balance baseline variables (108 matched patients for each group [i.e., delayed ablation and up-front ablation]). Patients were classified as having a low or high tumor burden score (TBS) on the basis of the number and size of the liver metastases. The primary outcome was progression-free survival (PFS); secondary outcomes included overall survival (OS), complications from ablation, and adverse events (AEs) from systemic therapy. Survival analysis used the Kaplan-Meier method. RESULTS. The median follow-up was 2.9 years. The 5-year PFS was 17.1% for delayed ablation versus 33.6% for up-front ablation in all patients and 17.9% versus 34.7% after PSM. Delayed ablation was associated with worse PFS in the crude analysis (HR = 0.62), IPTW analysis (HR = 0.66), and PSM analysis (HR = 0.62) (all p <.05). No analysis showed a significant difference in OS between delayed and up-front ablation. Crude, IPTW, and PSM analyses showed better PFS for up-front compared with delayed ablation in patients with a low TBS (HR = 0.62-0.67; all p <.05); none of these analyses showed significant difference in PFS in patients with a high TBS. Delayed ablation and up-front ablation groups showed no difference in frequency of grade III or IV ablation complications (4.7% vs 6.8%, p =.38) or grade III or IV systemic therapy AEs (12.4% vs 10.2%, p =.53). CONCLUSION. In patients with CLOM, up-front ablation achieved better PFS compared with delayed ablation, although only among patients with a low TBS. CLINICAL IMPACT. These findings could help optimize clinical implementation of thermal ablation in patients who are not candidates for surgical resection.